In recent years, demands for hot closed die forged products for middle- to large-sized aircrafts are markedly growing. Of these hot closed die forged products for middle- to large-sized aircrafts, for example, turbine disks for aircraft jet engines are made of a nickel alloy or titanium alloy, and they are concentric and have a diameter of greater than 1 meter. For producing these large-sized forged products, the deformation load during hot closed die forging requires a markedly high pressure more than 150 MN.
For example, hot forging dies most suitable for hot forging of large-sized forged products having a concentric form and high deformation resistance, such as turbine disks for aircraft jet engines and gas turbine disks for generation, have been produced by cutting out from a very large monolithic material block. As a result of this, the material blocks used to make the die has a weight of more than 5 tons, and the die is required to be produced from a large-sized steel ingot having a dissolution weight of more than 10 tons. In addition, many materials are scrapped during die-sinking, which presents the problem of poor productivity.
In order to solve the above-described problems, a method of producing a large-sized die assembled from a plurality of die pieces is proposed. For example, Japanese Patent Application Laid-Open (JP-A) No. 2009-66661 (Patent document 1) discloses a method of assembling and integrating a plurality of die pieces arranged in a radial pattern.